The present invention relates to optical gain media and, more particularly, to solid state gain media such as an optical fiber amplifier or cascaded optical fiber amplifiers a manner of pumping such amplifiers.
Optical fiber amplifiers receive coherent light of relatively low power from laser injection sources and amplify the light to higher power. Such amplifiers have been used in fiberoptic telecommunications and cable television systems to boost the power of a modulated optical signal being transmitted along a fiber transmission line. Erbium-doped fiber amplifiers (EDFAs) have been found to be especially convenient for fiber communication systems because their amplification wavelength (near 1.54 .mu.m) is conducive to low loss propagation of optical signals in glass transmission fibers. Various U.S. patents describe such systems, and the fiber amplifiers used by them, including but not limited to U.S. Pat. Nos. 5,185,826 (Delavaux); 5,218,608 (Aoki); 5,218,665 (Grasso et al.); 5,331,449 (Huber et al.); 5,337,175 (Ohnsorge et al.) and 5,339,183 (Suzuki). Various forms of signal modulation are used in these systems. Laser diode signal sources are capable of providing 10 mW to 100 mW, single mode, modulated light beams at high modulation rates, typically greater than 10 MHz, with low modulated drive currents. The modulated signal can then be amplified to higher powers, most typically up to about 100 mW, via the fiber amplifier.
This invention relates to the construct of the amplifiers and their associated pumping sources.